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Versions: 00 01 draft-ietf-netconf-with-defaults

NETCONF                                                       A. Bierman
Internet-Draft                                           Netconf Central
Intended status: Standards Track                              B. Lengyel
Expires: April 25, 2009                                         Ericsson
                                                        October 22, 2008


                  With-defaults capability for NETCONF
                 draft-bierman-netconf-with-defaults-01

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   The NETCONF protocol defines ways to read configuration data from a
   NETCONF agent.  Part of this data is not set by the NETCONF manager,
   but rather a default value is used.  In many situations the NETCONF
   manager has a priori knowledge about default data, so the NETCONF
   agent does not need to send it to the manager.  In other situations
   the NETCONF manger will need this data as part of the NETCONF rpc
   reply messages.  This document defines a capability-based extension



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   to the NETCONF protocol that allows the NETCONF manager to control
   whether default values are part of NETCONF rpc reply messages.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.1.  Requirements Notation  . . . . . . . . . . . . . . . .  3
       1.1.2.  NETCONF Terms  . . . . . . . . . . . . . . . . . . . .  3
   2.  With-defaults Capability . . . . . . . . . . . . . . . . . . .  4
     2.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  4
       2.1.1.  Basic handling of default data . . . . . . . . . . . .  4
     2.2.  Dependencies . . . . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Capability Identifier  . . . . . . . . . . . . . . . . . .  5
     2.4.  New Operations . . . . . . . . . . . . . . . . . . . . . .  5
     2.5.  Modifications to Existing Operations . . . . . . . . . . .  5
   3.  Interactions with Other Capabilities . . . . . . . . . . . . .  6
   4.  Data Model XSD . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   7.  Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Augmenting the base RPCs . . . . . . . . . . . . . . . . . 10
     7.2.  Other default handling methods in the real world?  . . . . 10
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
   Intellectual Property and Copyright Statements . . . . . . . . . . 13
























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1.  Introduction

   The NETCONF protocol defines ways to read configuration data from a
   NETCONF agent.  Part of this data is not set by the NETCONF manager,
   but rather a default value is used.  In many situations the NETCONF
   manager has a priori knowledge about default data, so the NETCONF
   agent does not need to send it to the manager.  A priori knowledge
   can be e.g. a document formally describing the data models supported
   by the NETCONF agent.

   A networking device may have a large number of default values.  Often
   the default values are not interesting or specifically defined with a
   "reasonable" value, so that the management user does not have to
   handle them.  For these reasons it is quite common for networking
   devices to suppress the output of parameters having the default
   value.

   However there are use-cases when a NETCONF manager will need the
   default data from the node:

   o  Documentation about default values can be unreliable or
      unavailable.
   o  Some management applications might not have the capabilities to
      correctly parse and interpret formal data models.
   o  Human users might want to understand the received data without
      consultation of the documentation.

   In all theses cases the NETCONF manager will need default data as
   part of the NETCONF rpc reply messages.

   This document defines a capability-based extension to the NETCONF
   protocol that allows the NETCONF manager to control whether default
   data is part of NETCONF rpc reply messages.

1.1.  Terminology

1.1.1.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

1.1.2.  NETCONF Terms

   o  Default data: Data that is set or used by the NETCONF agent
      whenever the NETCONF manager does not provide a specific value for
      the relevant data item.  In the context of this document only
      configuration data is considered, state data is excluded.



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   o  Explicitly set default data: Data that is explicitly set by the
      NETCONF manager to it's default value.  Some agents MIGHT treat
      explicitly set default data as simple default data, as they MIGHT
      not be able to differentiate between them.

   In addition the following terms are defined in RFC 4741 and are not
   redefined here:
   o  agent
   o  application
   o  manager
   o  operation
   o  RPC
   o  RPC request
   o  RPC response


2.  With-defaults Capability

2.1.  Overview

   The :with-defaults capability indicates that the NETCONF agent makes
   it possible for the NETCONF manager to control whether default data
   is part of NETCONF rpc reply messages.  The capability only effects
   configuration data not state data.  Sending of default data is
   controlled for each individual operation separately.  The NETCONF
   agent MUST also indicate it's basic behavior, whether it sends
   default data in the absence of any specific request from the NETCONF
   manager.

   This capability effects the <get>, <get-config> and <copy-config>
   operations.  Other operations that MIGHT return configuration data
   are not effected, unless this is specified in the document defining
   the respective operation.

2.1.1.  Basic handling of default data

   It is not defined in [RFC4741], whether default data is part of the
   datastore/data model, or if it is meta data, that influences the
   behavior of the NETCONF server, device but is not actually part of
   the datastore.  This document intentionally avoids deciding this
   question.

   As a consequence of this issue, NETCONF servers that do not implement
   the :with-defaults capability may or may not return default data in
   NETCONF rpc reply messages.
   Management agents report default data in different ways.  This
   document specifies the following three basic methods:




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   o  Report all: All default data is always reported.
   o  Trim: Values are not reported if they match the default.
   o  Explicit: Report values if they are explicitly set.

2.2.  Dependencies

   None

2.3.  Capability Identifier

   urn:ietf:params:netconf:capability:with-defaults

   The identifier MUST have an additional parameter: "basic".  This
   indicates how the agent reports default data in rpc reply messages,
   in the case the manager does not specify the required behavior in the
   rpc request.  The allowed values of this parameter are report-all,
   trim, explicit as defined in Section 2.1.1.  E.g.:

   urn:ietf:params:netconf:capability:with-defaults?basic=report-all

2.4.  New Operations

   None

2.5.  Modifications to Existing Operations

   A new 'with-defaults' XML attribute is used to control the reporting
   of default data.  If the 'with-defaults' attribute is present in the
   <rpc> element of the affected operations, the agent MUST return
   default data in the NETCONF rpc reply messages according to the value
   of the attribute.

   Allowed values of the with-defaults attribute are:
   o  false: indicates that default data will be returned as if the
      manager has omitted the attribute, using its basic handling method
      for defaults.  The basic behavior is indicated by the attribute on
      the capability.  See Section 2.3
   o  true: indicates that all default data MUST be returned.

   The 'with-defaults' attribute is defined in the namespace specified
   as the 'targetNamespace' in Section 4.  However, an agent MUST accept
   it even if no namespace is used.

   Affected operations:
   o  <get>
   o  <get-config>





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   o  <copy-config>

   The following example shows a <get> operation which is using the
   'with-defaults' attribute.  The manager is retrieving the
   'interfaces' object, defined in the example.com Interfaces data
   model.  (In this simple example, the 'name' field is defined as the
   key, and the 'mtu' field is the only other data in the <interface>
   element).  The default value of mtu is '1500'.  The basic default
   handling for the agent is "trim".  As the 'with-defaults' attribute
   is set to 'true', the mtu is returned not just for eth0 but also for
   eth1.



      <rpc message-id="102" with-defaults="true"
           xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
        <get>
          <filter type="subtree">
            <interfaces xmlns="http://example.com/interfaces/1.2"/>
          </filter>
        </get>
      </rpc>

      <rpc-reply message-id="102" with-defaults="true"
           xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
        <data>
          <interfaces xmlns="http://example.com/interfaces/1.2">
            <interface>
              <name>eth0</name>
              <mtu>8192</mtu>
            </interface>
            <interface>
              <name>eth1</name>
              <mtu>1500</mtu>
            </interface>
          </interfaces>
        </data>
      </rpc-reply>


                                 Figure 1


3.  Interactions with Other Capabilities

   None





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4.  Data Model XSD

   This section contains an XML Schema Definition
   [W3C.REC-xmlschema-2-20041028] which defines the XML syntax
   associated for the with-defaults XML attribute.



   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema xmlns="urn:ietf:params:xml:ns:netconf:with-defaults:1.0"
     targetNamespace="urn:ietf:params:xml:ns:netconf:with-defaults:1.0"
     xmlns:xs="http://www.w3.org/2001/XMLSchema"
     elementFormDefault="qualified" attributeFormDefault="unqualified"
     xml:lang="en">

     <xs:annotation>
       <xs:documentation>
         Schema defining the with-defaults attribute.

         Organization: "IETF NETCONF Working Group"
         Contact Info: balazs.lengyel@ericsson.com
       </xs:documentation>
     </xs:annotation>

     <xs:attribute name="with-defaults"
       type="xs:boolean"/>

   </xs:schema>



5.  IANA Considerations

   This document registers two URIs for the NETCONF XML namespace in the
   IETF XML registry [RFC3688].  Note that the capability URN is
   compliant to [RFC4741] section 10.3.

   +---------------+---------------------------------------------------+
   | Index         | Capability Identifier                             |
   +---------------+---------------------------------------------------+
   | :with-default | urn:ietf:params:netconf:capability:with-defaults: |
   | s             | 1.0                                               |
   +---------------+---------------------------------------------------+

   URI: urn:ietf:params:xml:ns:netconf:with-defaults:1.0

   Registrant Contact: The IESG.




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   XML: N/A, the requested URI is an XML namespace.


















































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6.  Security Considerations

   This document defines a minor extension to existing NETCONF protocol
   operations. it does not introduce any new or increased security risks
   into the management system.

   The 'with-defaults' capability provides manager controls over the
   retrieval of particular types of XML data from a configuration
   database.  They only suppress data that can already be retrieved with
   the standard protocol operations, and do not add any data to the
   configuration database.








































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7.  Open Issues

7.1.  Augmenting the base RPCs

   Instead of using an attribute on the RPC element we could "augment"
   the relevant NETCONF operations with an extra XML element with a
   similar meaning.

   Pro: parameters on RPC are for vendor extensions.  We should not put
   standard stuff there.

   Contra: Some people might consider this a violation of [RFC4741] as
   the XSD does not allow adding new elements.  As there is no NETCONF
   YAM (at least not yet), what do we actually augment?  Also there are
   multiple ways of defining RFC4741 in YANG.  The description will be
   perfectly clear, but it can never be fed into YANG tools.

   Conclusion: While augmenting has a certain elegance, we should stick
   to the attribute based solution.

7.2.  Other default handling methods in the real world?

   Are there any other basic default handling methods out there we need
   to include?



























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8.  Normative References

   [W3C.REC-xmlschema-2-20041028]
              Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes
              Second Edition", World Wide Web Consortium
              Recommendation REC-xmlschema-2-20041028, October 2004,
              <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.

   [RFC4741]  Enns, R., "NETCONF Configuration Protocol", RFC 4741,
              December 2006.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.



































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Authors' Addresses

   Andy Bierman
   Netconf Central
   Simi Valley, CA
   USA

   Email: andy@netconfcentral.com


   Balazs Lengyel
   Ericsson
   Budapest,
   Hungary

   Email: balazs.lengyel@ericsson.com



































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